CI: Add Ruby 4.0 preview2

Author: Watson1978

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
           - { full: 7.1.1-33, major-minor: '7.1' }
     name: Lint (Ruby ${{ matrix.ruby-version }}, ImageMagick ${{ matrix.imagemagick-version.major-minor }})
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         ref: ${{ github.event.pull_request.head.sha }}
     - name: Cache ImageMagick
@@ -56,7 +56,7 @@ jobs:
           - { full: 7.1.1-33, major-minor: '7.1' }
     name: Check RBS (Ruby ${{ matrix.ruby-version }}, ImageMagick ${{ matrix.imagemagick-version.major-minor }})
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         ref: ${{ github.event.pull_request.head.sha }}
     - name: Cache ImageMagick
@@ -87,13 +87,14 @@ jobs:
     runs-on: ubuntu-24.04
     timeout-minutes: 20
     strategy:
+      fail-fast: false
       matrix:
-        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4']
+        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4', '4.0.0-preview2']
         imagemagick-version:
           - { full: 7.1.1-33, major-minor: '7.1' }
     name: Ruby ${{ matrix.ruby-version }}
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Cache ImageMagick
       uses: actions/cache@v4
       with:
@@ -123,7 +124,7 @@ jobs:
         ruby-version: ['9.4.7.0']
     name: JRuby ${{ matrix.ruby-version }}
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up Ruby
       uses: ruby/setup-ruby@master
       with: